Recently there has been concerted effort among researchers and engineers to protect integrated chip circuitry from the troubling effect of natural background radiation. Natural background radiation, in the form of energetic alpha particles and neutrons, has become an increasingly difficult problem to solve as transistor size shrinks with each new generation of chips. High-energy particle irradiation can corrupt data stored in memory chips, producing what engineers refer to as "soft errors". As the semiconductor industry progresses toward line widths as fine as 0.18 microns, soft errors in data pose a major challenge.
A number of different approaches have been tried to reduce soft error rates in semiconductor devices. By way of example, U.S. Pat. No. 5,691,089 discloses a transistor device in which a doped layer of a radiation sensitive material is formed over a substrate. The radiation sensitive material may be polyamide or a similar organic dielectric. The inventors attribute improved alpha particle immunity to the complete isolation of the SRAM array by the organic dielectric layer.
A semiconductor memory array that reduces the probability of soft errors ascribable to alpha particles is also described in U.S. Pat. Nos. 5,365,478 and 5,732,037. These patents disclose a circuit solution applied to a dynamic random-access memory (DRAM). Another example is provided in U.S. Pat. No. 5,065,048, which teaches specialized precharging operations that enlarge the soft error margin against alpha particle strikes in CMOS and BiCMOS logic circuits. Yet another approach to the problem of soft errors in semiconductor memory devices is described in U.S. Pat. No. 5,301,146.
As will be seen, the present invention covers a generalized CMOS logic circuit that provides improved soft error immunity without added complexity or additional protection circuitry. The simple, elegant circuit approach offered by the invention can be advantageously employed in any CMOS logic gate having a storage node that is dominated by either N+ or P+ diffusion regions.